Aluminum selective etch

ABSTRACT

Methods of selectively etching aluminum and aluminum layers from the surface of a substrate are described. The etch selectively removes aluminum materials relative to silicon-containing films such as silicon, polysilicon, silicon oxide, silicon carbon nitride, silicon oxycarbide and/or silicon nitride. The methods include exposing aluminum materials (e.g. aluminum) to remotely-excited chlorine (Cl 2 ) in a substrate processing region. A remote plasma is used to excite the chlorine and a low electron temperature is maintained in the substrate processing region to achieve high etch selectivity. Aluminum oxidation may be broken through using a chlorine-containing precursor or a bromine-containing precursor excited in a plasma or using no plasma-excitation, respectively.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Prov. Pat. App. No. 61/903,240 filed Nov. 12, 2013, and titled “SELECTIVE ETCH FOR METAL-CONTAINING MATERIALS” by Ingle et al., which is hereby incorporated herein in its entirety by reference for all purposes.

FIELD

This invention relates to selectively removing aluminum.

BACKGROUND

Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective of the first material. As a result of the diversity of materials, circuits and processes, etch processes have been developed that selectively remove one or more of a broad range of materials.

Dry etch processes are often desirable for selectively removing material from semiconductor substrates. The desirability stems from the ability to gently remove material from miniature structures with minimal physical disturbance. Dry etch processes also allow the etch rate to be abruptly stopped by removing the gas phase reagents. Some dry-etch processes involve the exposure of a substrate to remote plasma by-products formed from one or more precursors. For example, remote plasma excitation of ammonia and nitrogen trifluoride enables silicon oxide to be selectively removed from a patterned substrate when the plasma effluents are flowed into the substrate processing region. Remote plasma etch processes have recently been developed to selectively remove a variety of dielectrics relative to one another. However, few dry-etch processes have been developed to selectively remove aluminum.

Methods are needed to selectively etch aluminum.

SUMMARY

Methods of selectively etching aluminum and aluminum layers from the surface of a substrate are described. The etch selectively removes aluminum materials relative to silicon-containing films such as silicon, polysilicon, silicon oxide, silicon carbon nitride, silicon oxycarbide and/or silicon nitride. The methods include exposing aluminum materials (e.g. aluminum) to remotely-excited chlorine (Cl₂) in a substrate processing region. A remote plasma is used to excite the chlorine and a low electron temperature is maintained in the substrate processing region to achieve high etch selectivity. Aluminum oxidation may be broken through using a chlorine-containing precursor or a bromine-containing precursor excited in a plasma or using no plasma-excitation, respectively.

Embodiments include methods of etching a patterned substrate. The methods include placing the patterned substrate in a substrate processing region of a substrate processing chamber. The patterned substrate includes an aluminum layer and a silicon-containing layer. The methods further include flowing a chlorine-containing precursor into a remote plasma region within the substrate processing chamber and exciting the chlorine-containing precursor in a remote plasma in the remote plasma region to produce plasma effluents. The remote plasma region is fluidly coupled with the substrate processing region through a showerhead. The methods further include flowing the plasma effluents into the substrate processing region through the showerhead. The methods further include selectively etching the aluminum layer.

Embodiments include methods of etching a substrate. The methods include placing the substrate in a substrate processing region of a substrate processing chamber. The substrate includes an aluminum oxide layer overlying an aluminum layer. The aluminum oxide layer consists of aluminum and oxygen. The methods further include flowing boron tribromide into the substrate processing region. The methods further include removing the aluminum oxide layer to expose the aluminum layer. The methods further include flowing molecular chlorine into a remote plasma region within the substrate processing chamber and exciting the molecular chlorine in a plasma in the remote plasma region to produce plasma effluents. The remote plasma region is fluidly coupled with the substrate processing region through a showerhead. The methods further include flowing the plasma effluents into the substrate processing region through the showerhead and selectively etching the aluminum layer.

Embodiments include methods of etching a substrate. The methods include placing the substrate in a substrate processing region of a substrate processing chamber. The substrate includes an aluminum oxide layer overlying an aluminum layer. The aluminum oxide layer consists of aluminum and oxygen and the aluminum layer consists of aluminum. The methods further include flowing boron trichloride into a remote plasma region within the substrate processing chamber and exciting the boron trichloride in a first plasma in the remote plasma region to produce first plasma effluents. The remote plasma region is fluidly coupled with the substrate processing region through a showerhead. The methods further include flowing the first plasma effluents through the showerhead into the substrate processing region and applying a local bias plasma power to further excite the first plasma effluents. The methods further include removing the aluminum oxide layer to expose the aluminum layer. The methods further include flowing molecular chlorine into the remote plasma region and exciting the molecular chlorine in a second plasma in the remote plasma region to produce second plasma effluents. The methods further include flowing the second plasma effluents into the substrate processing region through the showerhead. The methods further include selectively etching the aluminum layer.

Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed embodiments. The features and advantages of the disclosed embodiments may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the embodiments may be realized by reference to the remaining portions of the specification and the drawings.

FIG. 1 is a flow chart of an aluminum etch process according to embodiments.

FIG. 2 is a flow chart of an aluminum etch process according to embodiments.

FIG. 3A shows a schematic cross-sectional view of a substrate processing chamber according to embodiments.

FIG. 3B shows a schematic cross-sectional view of a portion of a substrate processing chamber according to embodiments.

FIG. 3C shows a bottom view of a showerhead according to embodiments.

FIG. 4 shows a top view of an exemplary substrate processing system according to embodiments.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

DETAILED DESCRIPTION

Methods of selectively etching aluminum and aluminum layers from the surface of a substrate are described. The etch selectively removes aluminum materials relative to silicon-containing films such as silicon, polysilicon, silicon oxide, silicon carbon nitride, silicon oxycarbide and/or silicon nitride. The methods include exposing aluminum materials (e.g. aluminum) to remotely-excited chlorine (Cl₂) in a substrate processing region. A remote plasma is used to excite the chlorine and a low electron temperature is maintained in the substrate processing region to achieve high etch selectivity. Aluminum oxidation may be broken through using a chlorine-containing precursor or a bromine-containing precursor excited in a plasma or using no plasma-excitation, respectively.

Etching aluminum has previously been accomplished by introducing boron trichloride and molecular chlorine into a substrate processing region housing a substrate. Local plasmas, including RIE and ICP modes, have been used to excite the boron trichloride/molecular chlorine mixture and accelerated ionized effluents toward the substrate. These local-plasma approaches enabled aluminum oxide to be removed and also enabled underlying aluminum to be etched without significant alterations to the process recipe. The drawback to these approaches was little to no selectivity. For example, this solely local plasma technique could only be expected to remove aluminum at about the same rate as, e.g., silicon oxide. Much higher selectivities are desirable and are enabled by the remote plasma techniques described herein.

In order to better understand and appreciate the invention, reference is now made to FIG. 1 which is a flow chart of an aluminum selective etch process 101 according to embodiments. The aluminum may or may not have an overlying aluminum oxide layer at the time of the first operation below. In the example below, no overlying oxidation layer exists at the time of etch process 101 initiation. The aluminum layer may consist essentially of or consist of aluminum in embodiments. The aluminum layer may be in the form of a blanket layer on the substrate or the aluminum layer may reside in discrete portions of a patterned substrate surface. In either case, the exemplary aluminum layer forms exposed surfaces on the substrate. The substrate is then delivered into a substrate processing region (operation 110).

A flow of molecular chlorine (Cl₂) is introduced into a remote plasma region separate from the processing region (operation 120). Other sources of chlorine may be used to augment or replace the molecular chlorine. In general, a chlorine-containing precursor may be flowed into the remote plasma region in embodiments. The chlorine-containing precursor may include one or more of atomic chlorine, molecular chlorine (Cl₂), hydrogen chloride (HCl), carbon tetrachloride (CCl₄) or boron trichloride (BCl₃) in embodiments. Molecular chlorine is used in preferred embodiments. The separate plasma region may be referred to as a remote plasma region herein and may be within a distinct module from the processing chamber or a compartment within the processing chamber. The separate plasma region may is fluidly coupled to the substrate processing region by through-holes in a showerhead disposed between the two regions. The hardware just described may also be used in all processes discussed herein.

The plasma effluents formed in the remote plasma region are then flowed into the substrate processing region (operation 130) through the through-holes the showerhead separating the remote plasma region and the substrate processing region. Aluminum on the substrate is selectively etched (operation 140) such that aluminum may be removed more rapidly than a variety of other exposed materials. For example, exposed aluminum may etch more rapidly than exposed silicon (e.g. poly), exposed silicon nitride or exposed silicon oxide. The reactive chemical species and any process effluents are removed from the substrate processing region and then the substrate is removed from the substrate processing region (operation 150).

The processes disclosed herein (FIG. 1 as well as FIG. 2 to be discussed shortly) display etch selectivities of aluminum relative to a variety of other materials. The aluminum may be selectively etched relative to a silicon-containing film which may also be present as exposed regions on the substrate. The silicon-containing layer may be silicon, silicon oxide, silicon nitride, silicon carbon nitride or silicon oxycarbide. The etch selectivity of aluminum relative to silicon (including single crystal, polysilicon or amorphous silicon) may be greater than or about 20:1, greater than or about 25:1, greater than or about 30:1 or greater than or about 40:1 in embodiments. The etch selectivity of aluminum relative to silicon nitride may be greater than or about 15:1, greater than or about 20:1, greater than or about 25:1 or greater than or about 30:1 in embodiments. The etch selectivity of an aluminum relative to silicon oxide may be greater than or about 20:1, greater than or about 25:1, greater than or about 30:1 or greater than or about 50:1 in embodiments. The etch selectivity of an aluminum relative to silicon carbon nitride may be greater than or about 15:1, greater than or about 25:1, greater than or about 30:1 or greater than or about 50:1 in embodiments. The etch selectivity of an aluminum relative to silicon oxycarbide may be greater than or about 15:1, greater than or about 25:1, greater than or about 30:1 or greater than or about 50:1 in embodiments. High etch selectivities of metal-containing materials relative to these materials provide advantages for a variety of devices, for example, whenever aluminum and aluminum oxide are to be removed without disturbing other features. The aluminum layer may consist of or consist essentially of aluminum in embodiments. The aluminum layer may be devoid of or essentially devoid of oxygen, carbon and/or nitrogen in embodiments.

The method also includes applying energy to the halogen-containing precursor in the remote plasma region to generate the plasma effluents. The plasma may be generated using known techniques (e.g., radio frequency excitations, capacitively-coupled power, inductively coupled power). In an embodiment, the energy is applied using a capacitively-coupled plasma unit. The remote plasma source power may be between about 100 watts and about 3000 watts, between about 200 watts and about 2000 watts, between about 300 watts and about 1000 watts in embodiments. In embodiments, the chlorine-containing precursor (e.g. Cl₂) is supplied at a flow rate of between about 5 sccm and about 500 sccm, between about 10 sccm and about 300 sccm, between about 25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm or between about 75 sccm and about 125 sccm.

Reference is now made to FIG. 2 which is a flow chart of an aluminum selective etch process 201 according to embodiments. In this example, an aluminum layer has a layer of oxidation on the surface which may be referred to herein as aluminum oxide. Prior to the first etch operation, aluminum oxide has been formed on a substrate, perhaps by exposure to atmosphere. Both the aluminum and the aluminum oxide may be in the form of a blanket layer on the substrate or the parallel layers may reside in discrete portions of a patterned substrate surface. In either case, the aluminum oxide forms exposed surfaces of the surface of the substrate. The substrate is then delivered into a substrate processing region (operation 210).

A flow of boron trichloride (BCl₃) is introduced into the remote plasma region (operation 220). Other sources of halogen may be used to augment or replace the boron trichloride. In general, a halogen-containing precursor, a bromine-containing precursor or a chlorine-containing precursor may be flowed into the remote plasma region in embodiments. The halogen-containing precursor may include one or more of atomic chlorine, atomic bromine, molecular bromine (Br₂), molecular chlorine (Cl₂), hydrogen chloride (HCl), hydrogen bromide (HBr), or boron trichloride (BCl₃) in embodiments. The halogen-containing precursor may be a boron-and-bromine-containing precursor according to embodiments, such as boron tribromide (BBr₃), BBr(CH₃)₂ or BBr₂(CH₃). The halogen-containing precursor may be a carbon-and-halogen-containing precursor according to embodiments, such as CBr₄ or CCl₄. The halogen-containing precursor may comprise boron, in embodiments, to further increase the etch selectivity relative to one or more of silicon, silicon oxycarbide, silicon carbon nitride, silicon oxide or silicon nitride.

Plasma excitation may be used to excite the halogen-containing precursor in some embodiments, and no plasma excitation is used in others. The exemplary boron trichloride is excited in the remote plasma region in operation 220. Plasma effluents are flowed from the remote plasma region through the showerhead and into the substrate processing region according to embodiments (operation 220). A local plasma is further used to excite the plasma effluents in operation 230. Local plasma parameters are provided following the description of the process flow.

Aluminum oxide on the substrate is selectively etched (operation 230) such that aluminum oxide may be removed more rapidly than a variety of other materials. The selective removal of aluminum oxide (e.g. Al₂O₃) may proceed by thermal means (without the assistance of a local or remote plasma exciting the boron tribromide) in embodiments. The reaction and removal of aluminum oxide with BCl₃ is endothermic and so a remote plasma and optional local plasma are used to provide enough energy for the reaction to proceed. The reaction and removal of aluminum oxide with BBr₃ is exothermic. In point of contrast, the reaction of BBr₃ with silicon is endothermic which enables a high Al₂O₃:Si etch selectivity for aluminum oxide selective etch process using BBr₃ in place of BCl₃. Boron tribromide is not passed through any plasma prior to entering the substrate processing region nor within the substrate processing region, according to embodiments, while etching aluminum oxide. Unused BCl₃ and any process effluents are removed from the substrate processing region. After operation 230, the aluminum layer is exposed within the substrate processing region.

A flow of molecular chlorine (Cl₂) is introduced into the remote plasma region (operation 240). Other sources of chlorine may be used to augment or replace the molecular chlorine. In general, a chlorine-containing precursor may be flowed into the remote plasma region in embodiments. The chlorine-containing precursor may include one or more of atomic chlorine, molecular chlorine (Cl₂), hydrogen chloride (HCl), carbon tetrachloride (CCl₄) or boron trichloride (BCl₃) in embodiments. Molecular chlorine is used in preferred embodiments. The separate plasma region may be referred to as a remote plasma region herein and may be within a distinct module from the processing chamber or a compartment within the processing chamber. The separate plasma region may is fluidly coupled to the substrate processing region by through-holes in a showerhead disposed between the two regions. The hardware just described may also be used in all processes discussed herein. The plasma effluents formed in the remote plasma region are then flowed into the substrate processing region (operation 240) through the through-holes the showerhead separating the remote plasma region and the substrate processing region. Aluminum on the substrate is selectively etched (operation 250) such that aluminum may be removed more rapidly than a variety of other exposed materials.

For example, exposed aluminum may etch more rapidly than exposed silicon (e.g. poly), exposed silicon nitride or exposed silicon oxide. The reactive chemical species and any process effluents are removed from the substrate processing region and then the substrate is removed from the substrate processing region (operation 260).

In embodiments, the halogen-containing precursor (e.g. BCl₃, Cl₂ or BBr₃) is supplied at a flow rate of between about 5 sccm and about 500 sccm, between about 10 sccm and about 300 sccm, between about 25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm or between about 75 sccm and about 125 sccm.

The aluminum oxide removal may proceed thermally, excited only by the temperature of the substrate itself, according to embodiments. The thermal-only example involves an exothermic reactions at the substrate surface. Alternatively, the aluminum oxide etching may include applying energy to the halogen-containing precursor in a remote plasma region to generate plasma effluents, which are then introduced into the substrate processing region in embodiments. FIG. 2 and associated discussion described describe both an exothermic and an endothermic example. Also alternatively, a local plasma may be used to excite the halogen-containing precursor. In the embodiments which include a plasma, the plasma may be generated using known techniques (e.g., radio frequency excitations, capacitively-coupled power, inductively coupled power). In an embodiment, the energy is applied using a capacitively-coupled plasma unit for either the remote plasma or the local plasma. In embodiments which rely on the temperature of the substrate to effect the etching reaction, the term “plasma-free” may be used herein to describe the substrate processing region during application using no or essentially no plasma power.

A local plasma is applied in some of the aluminum oxide etching operations described herein. The local plasma may be applied concurrently with the application of the remote plasma in embodiments. The local plasma may applied directly to the substrate processing region to create some local ion density and direct the low ion-density towards the substrate to accelerate the removal rate of the aluminum oxide. A plasma in the substrate processing region may also be referred to as a local plasma or a direct plasma. The local plasma may have a relatively low intensity compared with the remote plasma according to embodiments. The local plasma in the substrate processing region may be applied capacitively, in embodiments, and will be referred to herein as a bias plasma because ions are being directed towards the substrate. The bias plasma may be applied with a bias power which is less than about 20% of the remote plasma power, less than about 10% of the remote plasma power or less than about 5% of the remote plasma power in embodiments. In embodiments, the bias power may be less than or about 100 watts, less than or about 75 watts, less than or about 50 watts, less than or about 25 watts or essentially no bias power. The term “plasma-free” will be used herein to describe the substrate processing region during application of essentially no bias power. The high neutral radical density enables such a low bias power to be used productively to etch some aluminum layers with particular precursors.

The substrate temperatures described next apply to all the embodiments herein. The substrate temperature may be between 30° C. and 800° C. in embodiments. In embodiments, the temperature of the substrate during aluminum oxide etches described herein is greater than or 30° C., greater than or 50° C., greater than or 100° C., greater than or 150° C. or greater than or 200° C. The substrate temperatures may be less than or 400° C., less than or 350° C., less than or 325° C., less than or 300° C., and may be between 200° C. and 300° C. in embodiments. In other embodiments (e.g. using etchant BBr₃), the temperature of the substrate during aluminum oxide etches described herein may be between 300° C. and 800° C., preferably between 400° C. and 800° C., more preferably between 500° C. and 800° C. The temperature of the substrate during aluminum etches described herein may be between 20° C. and 200° C., between 30° C. and 150° C. or preferably between 60° C. and 120° C. according to embodiments.

The process pressures described next apply to all the embodiments herein, regardless of whether the process operations remove aluminum or aluminum oxide. The pressure within the substrate processing region is below 50 Torr, below 30 Torr, below 20 Torr, below 10 Torr or below 5 Torr. The pressure may be above 0.1 Torr, above 0.2 Torr, above 0.5 Torr or above 1 Torr in embodiments. In a preferred embodiment, the pressure while etching may be between 0.3 Torr and 10 Torr. However, any of the upper limits on temperature or pressure may be combined with lower limits to form additional embodiments.

For some materials and precursor combinations, the etch rate may drop in time and benefit from etch-purge-etch and etch-purge-etch cycles. This may be the case for boron-containing precursors used to etch at least aluminum oxide, but other materials may also display this effect. Therefore, the etching operations of all processes may have a pause in the flow of precursors to either the remote plasma or into the substrate processing region during the processes disclosed and claimed herein. The remote plasma region and/or the substrate processing region may be actively purged using a gas which displays essentially no chemical reactivity to the exposed materials on the patterned substrate. After purging the flows of precursors may be resumed to restart the removal of aluminum or aluminum oxide from the patterned substrate at a rejuvenated or renewed etch rate (which may be the same or similar to the initial etch rate of the etch process).

Aluminum oxide films contain aluminum and oxygen (and not just any specific example of stoichiometric aluminum oxide). The remote plasma etch processes may remove aluminum oxide which includes an aluminum atomic concentration greater than 20% and an oxygen atomic concentration greater than 60% in embodiments. The aluminum oxide may consist essentially of aluminum and oxygen, allowing for small dopant concentrations and other undesirable or desirable minority additives, in embodiments. Aluminum oxide may have roughly an atomic ratio 2:3 (Al:O). The aluminum oxide may contain between 30% and 50% aluminum and may contain between 50% and 70% oxygen in embodiments. Aluminum and aluminum layers may consist of or consist essentially of aluminum, allowing for small dopant concentrations as described in the context of aluminum oxide.

An advantage of the processes described herein lies in the conformal rate of removal of aluminum and aluminum oxide from the substrate. The methods do not rely on any (or at least a high bias power) to accelerate etchants towards the substrate, which reduces the tendency of the etch processes to remove material on the tops and bottom of trenches before material on the sidewalls can be removed. As used herein, a conformal etch process refers to a generally uniform removal rate of material from a patterned surface regardless of the shape of the surface. The surface of the layer before and after the etch process are generally parallel. A person having ordinary skill in the art will recognize that the etch process likely cannot be 100% conformal and thus the term “generally” allows for acceptable tolerances.

In each remote plasma or local plasma described herein, the flows of the precursors into the remote plasma region may further include one or more relatively inert gases such as He, N₂, Ar. The inert gas can be used to improve plasma stability, ease plasma initiation, and improve process uniformity. Argon is helpful, as an additive, to promote the formation of a stable plasma. Process uniformity is generally increased when helium is included. These additives are present in embodiments throughout this specification. Flow rates and ratios of the different gases may be used to control etch rates and etch selectivity.

In embodiments, an ion suppressor (which may be the showerhead) may be used to provide radical and/or neutral species for gas-phase etching. The ion suppressor may also be referred to as an ion suppression element. In embodiments, for example, the ion suppressor is used to filter etching plasma effluents en route from the remote plasma region to the substrate processing region. The ion suppressor may be used to provide a reactive gas having a higher concentration of radicals than ions. Plasma effluents pass through the ion suppressor disposed between the remote plasma region and the substrate processing region. The ion suppressor functions to dramatically reduce or substantially eliminate ionic species traveling from the plasma generation region to the substrate. The ion suppressors described herein are simply one way to achieve a low electron temperature in the substrate processing region during the gas-phase etch processes described herein.

In embodiments, an electron beam is passed through the substrate processing region in a plane parallel to the substrate to reduce the electron temperature of the plasma effluents. A simpler showerhead may be used if an electron beam is applied in this manner. The electron beam may be passed as a laminar sheet disposed above the substrate in embodiments. The electron beam provides a source of neutralizing negative charge and provides a more active means for reducing the flow of positively charged ions towards the substrate and increasing the etch selectivity in embodiments. The flow of plasma effluents and various parameters governing the operation of the electron beam may be adjusted to lower the electron temperature measured in the substrate processing region.

The electron temperature may be measured using a Langmuir probe in the substrate processing region during excitation of a plasma in the remote plasma. In aluminum removal embodiments, the electron temperature may be less than 0.5 eV, less than 0.45 eV, less than 0.4 eV, or less than 0.35 eV. These extremely low values for the electron temperature are enabled by the presence of the electron beam, showerhead and/or the ion suppressor. Uncharged neutral and radical species may pass through the electron beam and/or the openings in the ion suppressor to react at the substrate. Such a process using radicals and other neutral species can reduce plasma damage compared to conventional plasma etch processes that include sputtering and bombardment. Embodiments of the present invention are also advantageous over conventional wet etch processes where surface tension of liquids can cause bending and peeling of small features. In point of contrast, the electron temperature during the aluminum oxide removal process may be greater than 0.5 eV, greater than 0.6 eV or greater than 0.7 eV according to embodiments.

The substrate processing region may be described herein as “plasma-free” during the etch processes described herein. “Plasma-free” does not necessarily mean the region is devoid of plasma. Ionized species and free electrons created within the plasma region may travel through pores (apertures) in the partition (showerhead) at exceedingly small concentrations. The borders of the plasma in the chamber plasma region are hard to define and may encroach upon the substrate processing region through the apertures in the showerhead. Furthermore, a low intensity plasma may be created in the substrate processing region without eliminating desirable features of the etch processes described herein. All causes for a plasma having much lower intensity ion density than the chamber plasma region during the creation of the excited plasma effluents do not deviate from the scope of “plasma-free” as used herein.

FIG. 3A shows a cross-sectional view of an exemplary substrate processing chamber 1001 with a partitioned plasma generation region within the processing chamber. During film etching, a process gas may be flowed into chamber plasma region 1015 through a gas inlet assembly 1005. A remote plasma system (RPS) 1002 may optionally be included in the system, and may process a first gas which then travels through gas inlet assembly 1005. The process gas may be excited within RPS 1002 prior to entering chamber plasma region 1015. Accordingly, the chlorine-containing precursor as discussed above, for example, may pass through RPS 1002 or bypass the RPS unit in embodiments.

A cooling plate 1003, faceplate 1017, ion suppressor 1023, showerhead 1025, and a substrate support 1065 (also known as a pedestal), having a substrate 1055 disposed thereon, are shown and may each be included according to embodiments. Pedestal 1065 may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate. This configuration may allow the substrate 1055 temperature to be cooled or heated to maintain relatively low temperatures, such as between −20° C. to 200° C. Pedestal 1065 may also be resistively heated to relatively high temperatures, such as between 100° C. and 1100° C., using an embedded heater element.

Exemplary configurations may include having the gas inlet assembly 1005 open into a gas supply region 1058 partitioned from the chamber plasma region 1015 by faceplate 1017 so that the gases/species flow through the holes in the faceplate 1017 into the chamber plasma region 1015. Structural and operational features may be selected to prevent significant backflow of plasma from the chamber plasma region 1015 back into the supply region 1058, gas inlet assembly 1005, and fluid supply system 1010. The structural features may include the selection of dimensions and cross-sectional geometries of the apertures in faceplate 1017 to deactivate back-streaming plasma. The operational features may include maintaining a pressure difference between the gas supply region 1058 and chamber plasma region 1015 that maintains a unidirectional flow of plasma through the showerhead 1025. The faceplate 1017, or a conductive top portion of the chamber, and showerhead 1025 are shown with an insulating ring 1020 located between the features, which allows an AC potential to be applied to the faceplate 1017 relative to showerhead 1025 and/or ion suppressor 1023. The insulating ring 1020 may be positioned between the faceplate 1017 and the showerhead 1025 and/or ion suppressor 1023 enabling a capacitively coupled plasma (CCP) to be formed in the first plasma region.

The plurality of holes in the ion suppressor 1023 may be configured to control the passage of the activated gas, i.e., the ionic, radical, and/or neutral species, through the ion suppressor 1023. For example, the aspect ratio of the holes, or the hole diameter to length, and/or the geometry of the holes may be controlled so that the flow of ionically-charged species in the activated gas passing through the ion suppressor 1023 is reduced. The holes in the ion suppressor 1023 may include a tapered portion that faces chamber plasma region 1015, and a cylindrical portion that faces the showerhead 1025. The cylindrical portion may be shaped and dimensioned to control the flow of ionic species passing to the showerhead 1025. An adjustable electrical bias may also be applied to the ion suppressor 1023 as an additional means to control the flow of ionic species through the suppressor. The ion suppression element 1023 may function to reduce or eliminate the amount of ionically charged species traveling from the plasma generation region to the substrate. Uncharged neutral and radical species may still pass through the openings in the ion suppressor to react with the substrate.

Plasma power can be of a variety of frequencies or a combination of multiple frequencies. In the exemplary processing system the plasma may be provided by RF power delivered to faceplate 1017 relative to ion suppressor 1023 and/or showerhead 1025. The RF power may be between about 10 watts and about 5000 watts, between about 100 watts and about 2000 watts, between about 200 watts and about 1500 watts, or between about 200 watts and about 1000 watts in embodiments. The RF frequency applied in the exemplary processing system may be low RF frequencies less than about 200 kHz, high RF frequencies between about 10 MHz and about 15 MHz, or microwave frequencies greater than or about 1 GHz in embodiments. The plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the remote plasma region.

A precursor, for example a chlorine-containing precursor, may be flowed into substrate processing region 1033 by embodiments of the showerhead described herein. Excited species derived from the process gas in chamber plasma region 1015 may travel through apertures in the ion suppressor 1023, and/or showerhead 1025 and react with an additional precursor flowing into substrate processing region 1033 from a separate portion of the showerhead. Alternatively, if all precursor species are being excited in chamber plasma region 1015, no additional precursors may be flowed through the separate portion of the showerhead. Little or no plasma may be present in substrate processing region 1033 during the remote plasma etch process. Excited derivatives of the precursors may combine in the region above the substrate and/or on the substrate to etch structures or remove species from the substrate.

The processing gases may be excited in chamber plasma region 1015 and may be passed through the showerhead 1025 to substrate processing region 1033 in the excited state. While a plasma may be generated in substrate processing region 1033, a plasma may alternatively not be generated in the processing region. In one example, the only excitation of the processing gas or precursors may be from exciting the processing gases in chamber plasma region 1015 to react with one another in substrate processing region 1033. As previously discussed, this may be to protect the structures patterned on substrate 1055.

FIG. 3B shows a detailed view of the features affecting the processing gas distribution through faceplate 1017. The gas distribution assemblies such as showerhead 1025 for use in the processing chamber section 1001 may be referred to as dual channel showerheads (DCSH) and are additionally detailed in the embodiments described in FIG. 3A as well as FIG. 3C herein. The dual channel showerhead may provide for etching processes that allow for separation of etchants outside of the processing region 1033 to provide limited interaction with chamber components and each other prior to being delivered into the processing region.

The showerhead 1025 may comprise an upper plate 1014 and a lower plate 1016. The plates may be coupled with one another to define a volume 1018 between the plates. The coupling of the plates may be so as to provide first fluid channels 1019 through the upper and lower plates, and second fluid channels 1021 through the lower plate 1016. The formed channels may be configured to provide fluid access from the volume 1018 through the lower plate 1016 via second fluid channels 1021 alone, and the first fluid channels 1019 may be fluidly isolated from the volume 1018 between the plates and the second fluid channels 1021. The volume 1018 may be fluidly accessible through a side of the gas distribution assembly 1025. Although the exemplary system of FIGS. 3A-3C includes a dual-channel showerhead, it is understood that alternative distribution assemblies may be utilized that maintain first and second precursors fluidly isolated prior to substrate processing region 1033. For example, a perforated plate and tubes underneath the plate may be utilized, although other configurations may operate with reduced efficiency or not provide as uniform processing as the dual-channel showerhead as described.

In the embodiment shown, showerhead 1025 may distribute via first fluid channels 1019 process gases which contain plasma effluents upon excitation by a plasma in chamber plasma region 1015. In embodiments, the process gas introduced into RPS 1002 and/or chamber plasma region 1015 may contain chlorine, e.g., Cl₂ or BCl₃. The process gas may also include a carrier gas such as helium, argon, nitrogen (N₂), etc. Plasma effluents may include ionized or neutral derivatives of the process gas and may also be referred to herein as a radical-chlorine precursor referring to the atomic constituent of the process gas introduced.

FIG. 3C is a bottom view of a showerhead 1025 for use with a processing chamber in embodiments. Showerhead 1025 corresponds with the showerhead shown in FIG. 3A. Through-holes 1031, which show a view of first fluid channels 1019, may have a plurality of shapes and configurations to control and affect the flow of precursors through the showerhead 1025. Small holes 1027, which show a view of second fluid channels 1021, may be distributed substantially evenly over the surface of the showerhead, even amongst the through-holes 1031, which may help to provide more even mixing of the precursors as they exit the showerhead than other configurations.

The chamber plasma region 1015 or a region in an RPS may be referred to as a remote plasma region. In embodiments, the radical precursor, e.g., a radical-chlorine precursor, is created in the remote plasma region and travels into the substrate processing region where it may or may not combine with additional precursors. In embodiments, the additional precursors are excited only by the radical-chlorine precursor. Plasma power may essentially be applied only to the remote plasma region in embodiments to ensure that the radical-chlorine precursor provides the dominant excitation. Chlorine or another chlorine-containing precursor may be flowed into chamber plasma region 1015 at rates between about 5 sccm and about 500 sccm, between about 10 sccm and about 150 sccm, or between about 25 sccm and about 125 sccm in embodiments.

Combined flow rates of precursors into the chamber may account for 0.05% to about 20% by volume of the overall gas mixture; the remainder being carrier gases. The chlorine-containing precursor may be flowed into the remote plasma region, but the plasma effluents may have the same volumetric flow ratio in embodiments. In the case of the chlorine-containing precursor, a purge or carrier gas may be first initiated into the remote plasma region before the chlorine-containing gas to stabilize the pressure within the remote plasma region. Substrate processing region 1033 can be maintained at a variety of pressures during the flow of precursors, any carrier gases, and plasma effluents into substrate processing region 1033. The pressure may be maintained between 0.1 mTorr and 100 Torr, between 1 Torr and 20 Torr or between 1 Torr and 5 Torr in embodiments.

Embodiments of the dry etch systems may be incorporated into larger fabrication systems for producing integrated circuit chips. FIG. 4 shows one such processing system (mainframe) 1101 of deposition, etching, baking, and curing chambers in embodiments. In the figure, a pair of front opening unified pods (load lock chambers 1102) supply substrates of a variety of sizes that are received by robotic arms 1104 and placed into a low pressure holding area 1106 before being placed into one of the substrate processing chambers 1108 a-f. A second robotic arm 1110 may be used to transport the substrate wafers from the holding area 1106 to the substrate processing chambers 1108 a-f and back. Each substrate processing chamber 1108 a-f, can be outfitted to perform a number of substrate processing operations including the dry etch processes described herein in addition to cyclical layer deposition (CLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), etch, pre-clean, degas, orientation, and other substrate processes.

The substrate processing chambers 1108 a-f may be configured for depositing, annealing, curing and/or etching a film on the substrate wafer. In one configuration, all three pairs of chambers, e.g., 1108 a-f, may be configured to etch a film on the substrate, for example, chambers 1108 a-d may be used to etch the gapfill silicon oxide to create space for the airgap while chambers 1108 e-f may be used to etch the polysilicon.

In the preceding description, for the purposes of explanation, numerous details have been set forth to provide an understanding of various embodiments of the present invention. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.

As used herein “substrate” may be a support substrate with or without layers formed thereon. The patterned substrate may be an insulator or a semiconductor of a variety of doping concentrations and profiles and may, for example, be a semiconductor substrate of the type used in the manufacture of integrated circuits. Exposed “silicon” or “polysilicon” of the patterned substrate is predominantly Si but may include minority concentrations of other elemental constituents such as nitrogen, oxygen, hydrogen and carbon. Exposed “silicon” or “polysilicon” may consist of or consist essentially of silicon. Exposed “silicon nitride” of the patterned substrate is predominantly silicon and nitrogen but may include minority concentrations of other elemental constituents such as oxygen, hydrogen and carbon. “Exposed silicon nitride” may consist essentially of or consist of silicon and nitrogen. Exposed “silicon oxide” of the patterned substrate is predominantly SiO₂ but may include minority concentrations of other elemental constituents such as nitrogen, hydrogen and carbon. In embodiments, silicon oxide films etched using the methods taught herein consist essentially of or consist of silicon and oxygen. Analogous definitions will be understood for “aluminum”.

The term “precursor” is used to refer to any process gas which takes part in a reaction to either remove material from or deposit material onto a surface. “Plasma effluents” describe gas exiting from the chamber plasma region and entering the substrate processing region. Plasma effluents are in an “excited state” wherein at least some of the gas molecules are in vibrationally-excited, dissociated and/or ionized states. A “radical precursor” is used to describe plasma effluents (a gas in an excited state which is exiting a plasma) which participate in a reaction to either remove material from or deposit material on a surface. “Radical-chlorine” are radical precursors which contain chlorine but may contain other elemental constituents. The phrase “inert gas” refers to any gas which does not form chemical bonds when etching or being incorporated into a film. Exemplary inert gases include noble gases but may include other gases so long as no chemical bonds are formed when (typically) trace amounts are trapped in a film.

The terms “gap” and “trench” are used throughout with no implication that the etched geometry has a large horizontal aspect ratio. Viewed from above the surface, trenches may appear circular, oval, polygonal, rectangular, or a variety of other shapes. A trench may be in the shape of a moat around an island of material. The term “via” is used to refer to a low aspect ratio trench (as viewed from above) which may or may not be filled with metal to form a vertical electrical connection. As used herein, an isotropic or a conformal etch process refers to a generally uniform removal of material on a surface in the same shape as the surface, i.e., the surface of the etched layer and the pre-etch surface are generally parallel. A person having ordinary skill in the art will recognize that the etched interface likely cannot be 100% conformal and thus the term “generally” allows for acceptable tolerances.

Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosed embodiments. Additionally, a number of well-known processes and elements have not been described to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the dielectric material” includes reference to one or more dielectric materials and equivalents thereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups. 

The invention claimed is:
 1. A method of etching a patterned substrate, the method comprising: placing the patterned substrate in a substrate processing region of a substrate processing chamber, wherein the patterned substrate comprises an aluminum layer and a silicon-containing layer; flowing a chlorine-containing precursor into a remote plasma region within the substrate processing chamber and exciting the chlorine-containing precursor in a remote plasma in the remote plasma region to produce plasma effluents, wherein the remote plasma region is fluidly coupled with the substrate processing region through a showerhead; flowing the plasma effluents into the substrate processing region through the showerhead; and selectively etching the aluminum layer, wherein an electron temperature in the substrate processing region while selectively etching the aluminum layer is below 0.5 eV.
 2. The method of claim 1 wherein the chlorine-containing precursor is one of halogen-containing precursor comprises one or more of atomic chlorine, molecular chlorine (Cl₂), hydrogen chloride (HCl), carbon tetrachloride (CCl₄), or boron trichloride (BCl₃).
 3. The method of claim 1 wherein the aluminum layer and the silicon-containing layer are each exposed and selectively etching the aluminum layer comprises removing the aluminum layer at least fifteen times faster than the silicon-containing layer.
 4. The method of claim 1 wherein the silicon-containing layer comprises silicon oxide, silicon nitride, silicon carbon nitride or silicon oxycarbide.
 5. The method of claim 1 wherein the aluminum layer consists of aluminum.
 6. A method of etching a substrate, the method comprising: placing the substrate in a substrate processing region of a substrate processing chamber, wherein the substrate comprises an aluminum oxide layer overlying an aluminum layer, wherein the aluminum oxide layer consists of aluminum and oxygen; flowing boron tribromide into the substrate processing region; removing the aluminum oxide layer to expose the aluminum layer, wherein the boron tribromide is not passed through any plasma prior to entering the substrate processing region nor within the substrate processing region, while removing the aluminum oxide layer; flowing molecular chlorine into a remote plasma region within the substrate processing chamber and exciting the molecular chlorine in a plasma in the remote plasma region to produce plasma effluents, wherein the remote plasma region is fluidly coupled with the substrate processing region through a showerhead; flowing the plasma effluents into the substrate processing region through the showerhead; and selectively etching the aluminum layer.
 7. The method of claim 6 further comprising removing any process effluents between removing the aluminum oxide layer and flowing molecular chlorine.
 8. The method of claim 6 wherein the substrate processing region is plasma-free while removing the aluminum oxide layer and selectively etching the aluminum layer.
 9. The method of claim 6 wherein the boron tribromide is not passed through any plasma prior to entering the substrate processing region nor within the substrate processing region.
 10. The method of claim 6 wherein a pressure in the substrate processing region is greater than 0.1 Torr while removing the aluminum oxide layer.
 11. A method of etching a substrate, the method comprising: placing the substrate in a substrate processing region of a substrate processing chamber, wherein the substrate comprises an aluminum oxide layer overlying an aluminum layer, wherein the aluminum oxide layer consists of aluminum and oxygen and the aluminum layer consists of aluminum; flowing boron trichloride into a remote plasma region within the substrate processing chamber and exciting the boron trichloride in a first plasma in the remote plasma region to produce first plasma effluents, wherein the remote plasma region is fluidly coupled with the substrate processing region through a showerhead; flowing the first plasma effluents through the showerhead into the substrate processing region and applying a local bias plasma power to further excite the first plasma effluents; removing the aluminum oxide layer to expose the aluminum layer; flowing molecular chlorine into the remote plasma region and exciting the molecular chlorine in a second plasma in the remote plasma region to produce second plasma effluents; flowing the second plasma effluents into the substrate processing region through the showerhead; and selectively etching the aluminum layer, wherein an electron temperature in the substrate processing region while selectively etching the aluminum layer is below 0.5 eV.
 12. The method of claim 11 wherein a temperature of the substrate during both removing the aluminum oxide layer and removing the aluminum layer is between about 60° C. and about 120° C.
 13. The method of claim 11 wherein the substrate processing region is plasma-free while selectively etching the aluminum layer.
 14. The method of claim 11 wherein an electron temperature in the substrate processing region while removing the aluminum oxide layer is greater than 0.5 eV. 